Polymers as a class of materials are generally flammable. Owing to their combustibility, thermoplastic and thermoset polymers, for example polyamides, polyesters, epoxy resins and polyurethanes, require the use of flame retardants fir many applications. Typically, halogenated compounds, more specifically, aromatic polybrominated compounds, have been used as flame retardant additives in polymers. It is generally accepted that these products inhibit radical gas phase reactions from occurring in the flame when these products are ignited. This makes halogenated flame retardants very commonly used additives for different types of polymeric materials. However, during the last fifteen years or so, halogenated flame retardants have come under scrutiny because of ecological concerns. At this time, the flame retardant industry is under pressure to change to flame retardants that are perceived to be more environmentally friendly, such as organophosphorus flame retardants.
A wide variety of organophosphorus compounds have been shown in the prior art to impart flame retardancy to polymers. Most of the phosphorus-containing flame retardants provide flame retardant activity through a combination of vapor and condensed phase reactions, polymer carbonization promotion, and char formation. However, there are usually problems associated with the use of organophosphorus flame retardant materials. One source of difficulty relates to the processing of polymers, which often requires high temperatures, potentially at temperatures above 210° C. and often as high as 310-350° C. Unfortunately, flame retardants often participate in decomposition or side reactions, which impart undesirable properties to the base polymer or polymer system. Other flame retardants become too volatile under processing conditions and are not effectively retained during processing.
It is desirable therefore, to develop new flame retardants, which are thermally and hydrolytically stable and able to withstand high temperature polymer processing.